A memory system including a semiconductor nonvolatile memory (semiconductor memory) and a memory controller that controls the semiconductor nonvolatile memory is known. The memory system operates by receiving supply of power from the outside. The memory system may include an auxiliary power supply in order to make necessary data (e.g., dirty data), which is not yet in a state of being non-volatile, non-volatile after supply of power from the outside is cut off. That is, the memory system uses the auxiliary power supply to make necessary data, which is not yet in a state of being non-volatile, non-volatile. On the other hand, a period of time is limited for the memory system to be driven by the auxiliary power supply.